Redirected
1,304 views

2 Answers

5 votes
5 votes

SCAN (Elevator) : This approach works like an elevator does. It scans down towards the nearest end and then when it hits the bottom it scans up servicing the requests that it didn't get going down. If a request comes in after it has been scanned it will not be serviced until the process comes back down or moves back up.

2 , 6 , 10 , 20 , 22 , 38 , 40

Current Head is at 20

=> (22-20) + (38-22) + (40-38) + (40-10) + (10-6) + (6-2)

=> 2 + 16 + 2 + 30 + 4 + 4

=> 58 cylinders

58 cylinders * 6msec = 348 msec

Ans. (d)

                 

4 votes
4 votes
SCAN disk scheduling alorithm scans down towards the nearest end and then when it hits the bottom it scans up servicing the requests that it didn't get going down.

So, Requests are serviced in order : $20, 22, 38, 40, 10 ,6 , 2$

So, total disk movements $ = | 20- 20 | + | 20 -22 | + |22 - 38 | + |38 - 40| + |40 - 10| + |10 - 6| + |6-2|$

$\Rightarrow 0 + 2 + 16 + 2 + 30 + 4 + 4 = 58$

And each disk movement takes $6ms$. So, total Seek time $ = 58*6 = 348ms$

No related questions found